Image forming apparatus

ABSTRACT

A thermal printer includes a main frame having side plates, a platen roller rotatably supported in the main frame, a print head unit supported in the main unit so as to be pivotable between an image-forming state and a non-image forming state, a sheet case adapted to accommodate a sheet, and a contact portion that is attached to the print head unit so as to pivot together with the print head unit. The print head unit is pressed against the platen roller to convey a sheet therebetween when the print head unit is in the image-forming state. The sheet case is mounted in the main frame through an insertion part formed in one of the side plates. The contact portion contacts the sheet case from a second side plate side when the print head unit is in the image-forming state. It is possible to reduce the occurrence of printing defects.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus. Morespecifically, the present invention relates to an image formingapparatus that has a print head unit for printing.

2. Background Information

Image forming apparatuses that have a print head unit for printing havebeen known conventionally. For example, Japanese Patent ApplicationPublications Nos. 11-10925 and 10-58804 disclose such image formingapparatuses.

Japanese Patent Application Publication No. 11-10925 discloses a printerconfigured such that a ribbon cassette (ink sheet case) is fixedlypositioned within the printer, and a head unit is pressed against aplaten (a platen roller) by having a lever (locking member) that isattached to the head unit (print head unit) engage a locking pinprovided at the side plate of the printer (an example of an imageforming apparatus).

Also, Japanese Patent Application Publication No. 10-58804 discloses aheat transfer recording apparatus (image forming apparatus) in which alocking device (locking member) attached to a housing (frame) engages anink cartridge (ink sheet case), such that the ink cartridge is fixedlypositioned within the heat transfer recording apparatus.

A heat transfer printer is a known example of an image formingapparatus. FIG. 13 is a perspective view showing the entireconfiguration of a conventional example of a heat transfer printer. FIG.14 is a front view showing a locking member engaged with an ink sheetcase in the conventional example of a heat transfer printer shown inFIG. 13. The structure of an example of a conventional heat transferprinter will now be described with reference to FIGS. 13 and 14.

As shown in FIG. 13, a conventional heat transfer printer has a metalframe 101 having a first side surface 101 a and a second side surface101 b, a thermal head unit 102 for printing, a platen roller 103, aplaten roller bearing 104 for rotatably supporting the platen roller103, an ink sheet case 105 for accommodating ink sheets, a lockingmember 106 for fixedly positioning the ink sheet case 105 in place, ametal shaft 107, two press members 108, a drive gear 109, a motorbracket 110, and an intermediate gear 111. The drive gear 109 has asmall gear 109 a and a large gear 109 b made of a resin and pivots thepress member 108 on the first side surface 101 a of the frame 101.Furthermore, a motor bracket 110 is attached to the first side surface101 a.

The second side surface 101 b opposite the first side surface 101 a ofthe frame 101 is provided with an ink sheet insertion part 101 c throughwhich the ink sheet case 105 is mounted. A concavity 105 a that engagesthe engaging unit 106 a of the locking member 106 is provided at apredetermined location of this ink sheet case 105.

The locking member 106 has a supporting part 106 b, a plate spring 106c, and a gripping part 106 d, as shown in FIGS. 13 and 14. Thissupporting part 106 b is coupled to the second side surface 101 b of theframe 101 to pivotably support the locking member 106. Also, the platespring 106 c comes into contact with a bent section 101 d of the secondside surface 101 b of the frame 101, and urges the engaging unit 106 aof the locking member 106 downward. The gripping part 106 d isconfigured such that when the gripping part 106 d is brought upward whenthe urging force of the plate spring 106 c, the engaging unit 106 a isseparated from the concavity 105 a of the ink sheet case 105. Also, thebent section 101 d, which comes into contact with the plate spring 106 cof the locking member 106, is formed at the top of the second sidesurface 101 b of the frame 101. The first side surface 101 a and secondside surface 101 b of the frame 101 are provided with insertion holes101 e through which both ends of the shaft 107 are rotatably inserted,as shown in FIG. 13.

The thermal head unit 102 is mounted in between the first side surface101 a and the second side surface 101 b of the frame 101, so as to becapable of pivoting around the supporting shaft. A head bottom part 102a provided to the bottom of the thermal head unit 102 is disposed so asto face the platen roller 103. Bent parts 102 b pressed on by the pressmembers 108 are formed above both ends of the head bottom part 102 a ofthe thermal head unit 102. The thermal head unit 102 is normally urgedin a direction away from the platen roller 103 by an urging member (notshown in Figures).

The two press members 108 are unrotatably coupled to near the two endsof the shaft 107. Shaft supports 107 a are formed on both ends of theshaft 107, outside the portions to which the press members 108 arecoupled. These shaft supports 107 a are rotatably supported in theinsertion holes 101 e of the frame 101. Also, press springs 108 a thatapply pressure to the two bend-worked parts 102 b of the thermal headunit 102 are affixed to the two press members 108. Furthermore, thepress member 108 next to the first side surface 101 a of the frame 101is disposed so as to engage the small gear 109 a of the drive gear 109.The drive gear 109 is coupled to the first side surface 101 a of theframe 101, and transmits driving force from the intermediate gear 111 tothe press members 108. The driving force of a motor (not shown) istransmitted to the large gear 109 b of the drive gear 109 via theintermediate gear 111.

In the pressing operation for the platen roller 103 of the thermal headunit 102 in the conventional heat transfer printer described above, thedriving force of the motor (not shown) is transmitted to the pressmember 108 that is on the first side surface 101 a side of the frame 101via the intermediate gear 111 and the large gear 109 b and small gear109 a of the drive gear 109. Accordingly, the press member 108 on thefirst side surface 101 a side of the frame 101 thereby pivots whilebeing supported by the shaft 107. As a result, the bent part 102 b nextto the first side surface 101 a of the frame 101 is pressed on by thepress spring 108 a of the press member 108. Since the two press members108 are unrotatably coupled to near ends of the shaft 107, the shaft 107and the press member 108 on the second side surface 101 b side of theframe 101 pivot as a result of the pivoting of the press member 108 onthe first side surface 101 a side. The bent part 102 b on the secondside surface 101 b side of the frame 101 is thereby pressed on by thepress spring 108 a of the press member 108 next to the second sidesurface 101 b. As a result, the head bottom part 102 a of the thermalhead unit 102 is pressed on by the platen roller 103 against the urgingforce of the urging member (not shown).

In the conventional heat transfer printer shown in FIGS. 13 and 14, thelocking member 106 is mounted on the second side surface 101 b of theframe 101 in order to prevent the ink sheet case 105 from moving in thewidth direction of the thermal head unit 102 (the direction of the arrowE in FIG. 13). However, with this locking member 106, the engaging unit106 a separates from the concavity 105 a of the ink sheet case 105 whenthe gripping part 106 d being brought up, and the ink sheet case 105therefore moves in the width direction of the thermal head unit 102 (thedirection of the arrow E in FIG. 13) if the gripping part 106 d ismistakenly brought up during printing. In this case, printing defectstend to result.

Also, in the structure disclosed in Japanese Patent ApplicationPublication No. 11-10925, a locking member for securing the ink sheetcase in place in the image forming apparatus is coupled to the printhead unit. Therefore, the print head unit separates from the platenroller if the locking member is mistakenly released from a locking pin.In that case, printing defects result.

Also, in the structure disclosed in Japanese Patent ApplicationPublication No. 10-58804, a locking member for securing the ink sheetcase in place in the image forming apparatus engages the ink sheet case.Therefore, the ink sheet case moves relative to the image formingapparatus if the locking member is mistakenly released from the inksheet case. In that case also, printing defects result.

In view of the above, it will be apparent to those skilled in the artfrom this disclosure that there exists a need for an improved imageforming apparatus that overcomes the problems of the conventional art.This invention addresses this need in the art as well as other needs,which will become apparent to those skilled in the art from thisdisclosure.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an image formingapparatus that is capable of reducing the occurrence of printingdefects.

The image forming apparatus according to the first aspect of the presentinvention is adapted to form an image on a sheet, and includes a mainframe having first and second side plates, a platen roller rotatablysupported in the main frame, a print head unit supported in the mainunit so as to be pivotable between an image-forming state and anon-image forming state, a sheet case adapted to accommodate a sheet,and a contact portion that is attached to the print head unit so as topivot together with the print head unit. An insertion part is formed onthe second side plate. The print head unit is pressed against the platenroller to convey a sheet therebetween when the print head unit is in theimage-forming state. The sheet case is designed to be mounted in themain frame through the insertion part. The contact portion contacts thesheet case from a second side plate side when the print head unit is inthe image-forming state.

In the image forming apparatus according to the first aspect of thepresent invention, the print head unit is provided with a contact unitthat contacts the sheet case from the second side plate during theprinting operation. Thus, it is possible to prevent the sheet case frommoving relative to the print head unit with the contact unit of theprint head unit. It is thereby possible to reduce the occurrence ofprinting defects.

In the image forming apparatus according to second aspect of the presentinvention, the sheet case includes a sheet feeder, a sheet take-up unit,and a linking unit that links the sheet feeder and the sheet take-upunit. The contact portion comes into contact with the linking unit ofthe sheet case when the print head unit is in the image-forming state.With such configuration, the sheet case can be easily prevented frommoving relative to the print head unit.

In the image forming apparatus according to the third aspect of thepresent invention, at least one of the contact unit and the linking unitof the sheet case is elastically deformed when the print head unit is inthe image-forming state and the contact unit is in contact with thelinking unit of the sheet case. With such configuration, the print headunit can be pressed toward the first side plate due to the urging forcefrom the elastic deformation of at least one of the linking unit and thecontact unit of the ink sheet case. It is thereby possible to preventthe print head unit from moving toward the opposite second side plate.Therefore, the occurrence of printing defects resulting from positioningmisalignments of the print head unit can be further reduced.

In the image forming apparatus according to the fourth aspect of thepresent invention, a guide unit that is coupled to the print head unitand is adapted to guide the sheet being conveyed is further provided.The contact portion is formed unitarily with the guide unit. With suchconfiguration, the number of components does not increase even though acontact unit is provided.

In the image forming apparatus according to the fifth aspect of thepresent invention, a locking member that is provided in the second sideplate of the main frame and designed to disengageably engage the sheetcase is further provided. In this case, the locking member is providedto prevent the sheet case from moving toward the second side plate. Inthe present invention, however, even when the engagement of the lockingmember with the sheet case and the second side plate is inadvertentlyreleased during the printing operation, it is still possible to preventthe sheet case from moving toward the second side plate relative to theprint head unit due to the contact of the contact unit of the print headunit. It is thereby possible to reduce the occurrence of printingdefects.

In the image forming apparatus according to the sixth aspect of thepresent invention, at least one of the contact unit and the sheet caseis elastically deformed when the print head unit is in the image-formingstate and the contact unit is in contact with the sheet case.

In the image forming apparatus according to the seventh aspect of thepresent invention, a guide unit that is coupled to the print head unitand is adapted to guide the sheet being conveyed is further provided.The contact portion is formed unitarily with the guide unit. The contactunit is elastically deformed when the print head unit is in theimage-forming state and the contact unit is in contact with the sheetcase.

In the image forming apparatus according to the eighth aspect of thepresent invention, the contact portion has a tapered part that decreasesits thickness in a downward direction.

In the image forming apparatus according to the eighth aspect of thepresent invention, the print head unit is a thermal head, and the imageforming apparatus is a heat transfer printer.

These and other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a perspective view of the entire configuration of the heattransfer printer according to one embodiment of the present inventionviewed from the second side plate side;

FIG. 2 is a perspective view of the entire configuration of the heattransfer printer according to the embodiment of the present inventionviewed from the first side plate side;

FIG. 3 is a plan view of the heat transfer printer shown in FIGS. 1 and2 according to the embodiment of the present invention;

FIG. 4 is a partial perspective view of the detailed structure of thecontact unit of the heat transfer printer shown in FIGS. 1 and 2according to the embodiment of the present invention;

FIG. 5 is a partial perspective view for of the contact unit and thepaper guide member of the heat transfer printer shown in FIGS. 1 and 2according to the embodiment of the present invention;

FIG. 6 is a schematic side elevational view of the heat transfer printershown in FIGS. 1 and 2 according to the embodiment of the presentinvention, showing a printing state in which the contact unit is incontact with the linking unit of the ink sheet case;

FIG. 7 is a partial cross-sectional view of the heat transfer printeraccording to the embodiment of the present invention viewed along theline VII—VII in FIG. 6;

FIG. 8 is a schematic side elevational view of the heat transfer printershown in FIGS. 1 and 2 according to the embodiment of the presentinvention, showing a non-printing state in which the contact unit is notin contact with the linking unit of the ink sheet case;

FIG. 9 is a partial cross-sectional view of the heat transfer printeraccording to the embodiment of the present invention viewed along theline IX—IX in FIG. 8;

FIG. 10 is a schematic side elevational view of the heat transferprinter shown in FIGS. 1 and 2 according to the embodiment of thepresent invention, showing the locking member being engaged with the inksheet case;

FIG. 11 is a schematic side elevational view of the heat transferprinter shown in FIGS. 1 and 2 according to the embodiment of thepresent invention, showing the locking member being released from theengagement with the ink sheet case;

FIG. 12 is a partial cross-sectional view showing the detailed structureof the contact unit according to another embodiment of the presentinvention;

FIG. 13 is a perspective view showing the entire configuration of aconventional example of a heat transfer printer; and

FIG. 14 is a front view showing the locking member in the conventionalheat transfer printer shown in FIG. 13, in which the locking member isengaged with the ink sheet case.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments of the present invention will now be explained withreference to the drawings. It will be apparent to those skilled in theart from this disclosure that the following descriptions of theembodiments of the present invention are provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

Embodiments of the present invention will now be described withreference to the diagrams.

FIGS. 1 and 2 are perspective views showing the entire configuration ofa heat transfer printer according to one embodiment of the presentinvention. FIG. 3 is a plan view of the heat transfer printer accordingto the embodiment shown in FIGS. 1 and 2. FIG. 4 is a perspective viewfor describing the detailed structure of the contact unit of the heattransfer printer according to the embodiment shown in FIGS. 1 and 2.FIGS. 5 through 12 are diagrams showing the detailed structure of theheat transfer printer according to the embodiment shown in FIGS. 1 and2.

First, the structure of the heat transfer printer according to theembodiment of the present invention will be described with reference toFIGS. 1 through 12. In the present embodiment, a heat transfer printerwill be discussed as one example of the image forming apparatus of thepresent invention.

As shown in FIG. 1, the heat transfer printer according to theembodiment of the present invention has a metal frame 1 having a firstside surface 1 a and a second side surface 1 b, a thermal head unit 2for printing, a platen roller 3, a platen roller bearing 4 forrotatively supporting the platen roller 3, an ink sheet case 5 made of aresin for accommodating ink sheets, and a locking member 6 fordisengageably engaging the ink sheet case 5 and the second side surface1 b and supporting the ink sheet case 5 to the second side surface 1 b.The thermal head unit 2 is supported to the main frame 1 so as to bepivotable between the printing position shown in FIG. 6 and non-printingposition shown in FIG. 8. The thermal head unit 2 is pressed against theplaten roller 3, conveying the ink sheet therebetween during theprinting operation.

As shown in FIG. 3, the heat transfer printer also has an ink sheetfeeder support member 7 and an ink sheet take-up member 8 on which theink sheet case 5 is mounted, as well as a metallic supporting rod 9, ametallic pivot member 10, a drive gear 11 for pivoting the pivot member10, a motor bracket 12, a motor 13 with a motor shaft gear 13 a, anintermediate gear 14 having a large gear 14 a that engages the motorshaft gear 13 a and a small gear 14 b that engages the drive gear 11, apaper guide member 15 (see FIG. 2) made of a resin, and a torsion coilspring 16. The thermal head unit 2 is an example of a “print head unit”of the present invention, the locking member 6 is an example of the“locking member” of the present invention, and the paper guide member 15is an example of the “guide unit” of the present invention.

As shown in FIG. 1, an ink sheet insertion part 1 c, through which theink sheet case 5 is mounted in between the first and the second sidesurfaces 1 a and 1 b of the main frame 1, is provided at the second sidesurface 1 b which is opposite the first side surface 1 a. The motorbracket 12 of the frame 1 is mounted on the first side surface 1 a.

The ink sheet case 5 has an ink sheet feeder 5 a, an ink sheet take-upunit 5 b, and a linking unit 5 c for linking the ink sheet feeder 5 aand the ink sheet take-up unit 5 b. The ink sheet feeder 5 a and the inksheet take-up unit 5 b are mounted on the ink sheet feeder supportmember 7 and the ink sheet take-up member 8, respectively, as shown inFIG. 3. The ink sheet feeder support member 7 and the ink sheet take-upmember 8 are provided with compression coil springs 7 a and 8 a forurging the ink sheet case 5 towards the second side surface 1 b. Aconcavity 5 d is formed at a specific location in the linking unit 5 cof the ink sheet case 5 as shown in FIG. 10, such that the engaging unit6 a of the locking member 6 engages the concavity 5 d.

The engaging unit 6 a of the locking member 6 is formed in a taperedshape such that its thickness decreases downward, as shown in FIG. 1.Accordingly, when the ink sheet case 5 is inserted into the ink sheetinsertion part 1 c of the frame 1, the locking member 6 pivots in thedirection of the arrow D around a supporting unit 6 b as shown in FIG.11, and the linking unit 5 c of the ink sheet case 5 comes into contactwith the tapered surface of the engaging unit 6 a of the locking member6. When the ink sheet case 5 is inserted up to a specific position, theengaging unit 6 a of the locking member 6 engages the concavity 5 d ofthe ink sheet case 5, as shown in FIG. 10.

The locking member 6 also has a supporting unit 6 b, a plate spring 6 c,and a gripping part 6 d. This supporting unit 6 b is mounted on thesecond side surface 1 b of the frame 1, and pivotably supports thelocking member 6. Also, the plate spring 6 c comes into contact with abent section 1 d of the second side surface 1 b of the frame 1, andurges the engaging unit 6 a of the locking member 6 downward. Thegripping part 6 d is configured such that when it is brought upwardagainst the urging force of the plate spring 6 c, the engaging unit 6 ais released from the engagement with the concavity 5 d of the ink sheetcase 5, as shown in FIG. 11. The ink sheet case 5 can thereby be removedfrom the ink sheet insertion part 1 c of the frame 1. Also, the bentsection 1 d with which the plate spring 6 c of the locking member 6comes into contact is formed at the top of the second side surface 1 bof the frame 1.

Cut-out parts 1 e for rotatably supporting the supporting shaft 2 a ofthe thermal head unit 2 are formed in the inner sides of the first sidesurface 1 a and the second side surface 1 b of the frame 1, as shown inFIG. 3. The torsion coil spring 16 for urging the thermal head unit 2 ina direction away from the platen roller 3 is mounted on the supportingshaft 2 a of the thermal head unit 2 next to the first side surface 1 aof the frame 1. Also, the head bottom part 2 b formed at the bottom ofthe thermal head unit 2 is disposed facing the platen roller 3 so as tohold ink sheets (not shown) between itself and the platen roller 3during the printing operation, as shown in FIG. 6.

In the present embodiment, the paper guide member 15 made of a resin forguiding the paper being conveyed is coupled to the thermal head unit 2with a screw 30, as shown in FIGS. 2 and 4. The paper guide member 15 isunitarily formed with a contact unit 15 a having a slanted part 15 bthat tapers off downward decreasing its thickness, as shown in FIG. 5.When the pivot member 10 is pressed and pivoted from the non-printingstate shown in FIGS. 8 and 9 to the printing operation state in FIGS. 6and 7, it is possible to allow the contact unit 15 a to engage thelinking unit 5 c of the ink sheet case 5 smoothly because of the slantedpart 15 b of the contact unit 15 a.

The contact unit 15 a made of a resin has a thickness (shown as W1 inFIG. 7) of about 2 mm, as shown in FIG. 7. The contact unit 15 a isconfigured so as to come into contact with the inner side of the linkingunit 5 c of the ink sheet case 5 during the printing operation. Whilethe linking unit 5 c engages the contact unit 15 a, the linking unit 5 cof the ink sheet case 5 that is made of a resin is designed toelastically deflect outward by about 0.2 mm to 0.3 mm (which is shown asW2 in FIG. 7). The paper guide member 15 is thereby pressed towards thesecond side surface 1 b of the frame 1 as shown in FIG. 3 by the urgingforce of the linking unit 5 c. Therefore, the thermal head unit 2 ispressed towards the second side surface 1 b of the frame 1 and comesinto contact with the cut-out parts 1 e of the frame 1.

Also, both ends of the supporting rod 9 are rotatably inserted intoinsertion holes 1 f in the first side surface 1 a and the second sidesurface 1 b of the frame 1, as shown in FIG. 2. The pivot member 10 isformed into a square-like shape having a first arm 10 a and a second arm10 b. Holes 10 c for mounting the supporting rod 9 are formed in thefirst arm 10 a and the second arm 10 b of the pivot member 10. Also, acam pin 10 d is formed in the first arm 10 a of the pivot member 10.This cam pin 10 d is disposed so as to engage a cam groove 11 a in thedrive gear 11 mounted on the first side surface 1 a of the frame 1, asshown in FIG. 1. Also, a pressing unit 10 e is provided in the secondarm 10 b of the pivot member 10. This pressing unit 10 e is disposed soas to apply pressure on the thermal head 2 at near the width direction(the direction of the arrow A in FIG. 1) center of the thermal head 2 bypivoting.

Also, the drive gear 11 is mounted on the first side surface 1 a of theframe 1 and is made to engage the small gear 14 b of the intermediategear 14, as shown in FIG. 3. The cam groove 11 a (see FIG. 1) forengaging the cam pin 10 d in the first arm 10 a of the pivot member 10is formed in the side of the drive gear 11. Also, the driving force ofthe motor 13 is transmitted to the drive gear 11 via the motor shaftgear 13 a and the intermediate gear 14.

Printing Operation

Next, the pressing operation for the platen roller 3 of the thermal headunit 2 in the heat transfer printer according to the present embodimentof the present invention will be described with reference to FIGS. 1, 3,6, and 8.

First, in the initial state, the thermal head unit 2 is pivoted in adirection away from the platen roller 3 (the direction of the arrow C)by the urging force of the torsion coil spring 16, as shown in FIG. 8.Here, the contact unit 15 a of the paper guide member 15 is locatedabove the linking unit 5 c of the ink sheet case 5. From this state, thedriving force of the motor 13 is transmitted to the drive gear 11 fromthe motor shaft gear 13 a via the large gear 14 a and the small gear 14b of the intermediate gear 14, as shown in FIG. 3. The driving force istransmitted from the cam groove 11 a of the drive gear 11 to the firstarm 10 a of the pivot member 10 via the cam pin 10 d of the pivot member10, as shown in FIG. 1. Thereby, the first arm 10 a of the pivot member10 pivots in the direction of the arrow B, and the second arm 10 b ofthe pivot member 10 also pivots in the direction of the arrow B.Accordingly, the pressing unit 10 e of the second arm 10 b of the pivotmember 10 presses on the thermal head unit 2, as shown in FIG. 6. Thehead bottom part 2 b of the thermal head unit 2 is thereby pressedagainst the platen roller 3 in spite of the urging force of the torsioncoil spring 16. Also, the contact unit 15 a of the paper guide member 15comes into contact with the inner side of the linking unit 5 c of theink sheet case 5.

In the present embodiment, as described above, the locking member 6 isprovided with an engaging unit 6 a that secures the ink sheet case 5 inplace and also engages the ink sheet case 5. Also, the paper guidemember 15 that is mounted on the thermal head unit 2 is provided withthe contact unit 15 a for preventing the ink sheet case 5 from movingduring the printing operation. Therefore, even when the engaging unit 6a of the locking member 6 is inadvertently released from the concavity 5d of the ink sheet case 5 due to the locking member 6 being brought upby mistake during the printing operation, it is possible to prevent theink sheet case 5 from being moved relative to the thermal head unit 2because of the contact unit 15 a of the paper guide member 15 mounted onthe thermal head unit 2. It is thereby possible to reduce the occurrenceof printing defects.

Also, in the present embodiment, the ink sheet case 5 is provided withthe ink sheet feeder 5 a, the ink sheet take-up unit 5 b, and thelinking unit 5 c that links the ink sheet feeder 5 a with the ink sheettake-up unit 5 b. The contact unit 15 a is designed to come into contactwith the linking unit 5 c of the ink sheet case 5 during the printingoperation. Accordingly, it is possible to easily prevent the ink sheetcase 5 from moving relative to the thermal head unit 2.

Also, in the present embodiment, at least one of the linking unit 5 c ofthe ink sheet case 5 and the contact portion 15 a of the paper guidemember 15 is designed to be deflected where the contact unit 15 a of thepaper guide member 15 comes into contact with the linking unit 5 c ofthe ink sheet case 5. Accordingly, the thermal head unit 2 can bepressed towards the first side plate 1 a by the urging force from theflexural deformation of the linking unit 5 c of the ink sheet case 5.The thermal head unit 2 can thereby be prevented from moving toward thesecond side plate 1 b. As a result, it is possible to reducenon-uniformities in printed image due to positioning misalignments inthe thermal head unit 2.

Also, in the present embodiment, the paper guide member 15 for guidingpaper is provided to the thermal head unit 2, and the contact unit 15 ais formed integrally with the paper guide member 15. Therefore, there isno increase in the number of components even though the contact unit 15a is additionally provided.

Other Embodiments

The embodiment currently disclosed should be considered as merely anexample in all respects and not as being restrictive. The range of thepresent invention is expressed by the patent claims and not by the abovedescription of the embodiment, and further includes meanings equivalentto the range of the patent claims and all variations within this range.

(a) For example, in the embodiment described above, a heat transferprinter is given as an example of an image forming apparatus. However,the present invention is not limited to such construction, and can alsobe applied to image forming apparatuses other than a heat transferprinters as long as such image forming apparatus has a print head unitfor printing.

(b) Also, in the embodiment described above, the contact unit 15 a wasformed unitarily with the paper guide unit 15. However, the presentinvention is not limited to such construction, and the contact unit maybe provided separately from the paper guide unit.

(c) Also, in the embodiment described above, the contact unit 15 a isbrought into contact with the linking unit 5 c of the ink sheet case 5.However, the present invention is not limited to such construction, andthe contact unit can also be brought into contact with the ink sheetfeeder 5 a or the ink sheet take-up unit 5 b of the ink sheet case 5.The contact unit can also be brought into contact with other portions ofthe ink sheet case.

(d) Also, in the embodiment described above, the linking unit 5 c of theink sheet case 5 is elastically bended and deformed during the printingoperation. However, the present invention is not limited to suchconstruction. As shown in FIG. 12, a paper guide member 25 made of aresin may be provided with a contact unit 25 a having a structure thatis shaped as a plate spring and is prone to elastic deformation, asshown in FIG. 12. In this case, the linking unit 5 c of the ink sheetcase 5 may either be configured so as to bend or not to bend. In thiscase, the contact unit 25 a is preferably formed so as to have a slantedpart 25 b that tapers off decreasing its thickness in a downwarddirection as shown in FIG. 12.

Here, in view of the similarity between the first and the precedingembodiments, the parts of the two embodiments that are identical aregiven the same reference numerals as the parts of the first embodiment.Moreover, the descriptions of the parts that are identical to the partsof the first embodiment are omitted for the sake of brevity.

As used herein, the following directional terms “forward, rearward,above, downward, vertical, horizontal, below and transverse” as well asany other similar directional terms refer to those directions of adevice equipped with the present invention. Accordingly, these terms, asutilized to describe the present invention should be interpretedrelative to a device equipped with the present invention.

The term “configured” as used herein to describe a component, section orpart of a device includes hardware and/or software that is constructedand/or programmed to carry out the desired function.

Moreover, terms that are expressed as “means-plus function” in theclaims should include any structure that can be utilized to carry outthe function of that part of the present invention.

The terms of degree such as “substantially”, “about” and “approximately”as used herein mean a reasonable amount of deviation of the modifiedterm such that the end result is not significantly changed. For example,these terms can be construed as including a deviation of at least ±5% ofthe modified term if this deviation would not negate the meaning of theword it modifies.

This application claims priority to Japanese Patent Application No.2004-173391. The entire disclosure of Japanese Patent Application No.2004-173391 is hereby incorporated herein by reference.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents. Thus, the scope ofthe invention is not limited to the disclosed embodiments.

1. An image forming apparatus adapted to form an image on a sheet,comprising: a main frame having first and second side plates, aninsertion part being formed on the second side plate; a platen rollerrotatably supported in the main frame; a print head unit supported inthe main unit so as to be pivotable between an image-forming state and anon-image forming state, the print head unit being pressed against theplaten roller to convey a sheet therebetween when the print head unit isin the image-forming state; a sheet case adapted to accommodate a sheet,the sheet case being designed to be mounted in the main frame throughthe insertion part; and a contact portion that is attached to the printhead unit so as to pivot together with the print head unit, the contactportion contacting the sheet case from a second side plate side when theprint head unit is in the image-forming state.
 2. The image formingapparatus according to claim 1, wherein the sheet case includes a sheetfeeder, a sheet take-up unit, and a linking unit that links the sheetfeeder and the sheet take-up unit, and the contact portion comes intocontact with the linking unit of the sheet case when the print head unitis in the image-forming state.
 3. The image forming apparatus accordingto claim 1, wherein at least one of the contact portion and the linkingunit of the sheet case is elastically deformed when the print head unitis in the image-forming state and the contact portion is in contact withthe linking unit of the sheet case.
 4. The image forming apparatusaccording to claim 1, further comprising a guide unit that is coupled tothe print head unit and is adapted to guide the sheet being conveyed,wherein the contact portion is formed unitarily with the guide unit. 5.The image forming apparatus according to claim 1, further comprising alocking member that is provided in the second side plate of the mainframe and designed to disengageably engage the sheet case.
 6. The imageforming apparatus according to claim 1, wherein at least one of thecontact portion and the sheet case is elastically deformed when theprint head unit is in the image-forming state and the contact portion isin contact with the sheet case.
 7. The image forming apparatus accordingto claim 6, further comprising a guide unit that is coupled to the printhead unit and is adapted to guide the sheet being conveyed, wherein thecontact portion is formed unitarily with the guide unit, and the contactportion is elastically deformed when the print head unit is in theimage-forming state and the contact portion is in contact with the sheetcase.
 8. The image forming apparatus according to claim 7, wherein thecontact portion has a tapered part that decreases its thickness in adownward direction.
 9. The image forming apparatus according to claim 1,wherein the print head unit is a thermal head, and the image formingapparatus is a heat transfer printer.
 10. An image forming apparatusadapted to form an image on a sheet, comprising a main frame havingfirst and second side plates, an insertion part being formed on thesecond side plate; a platen roller rotatably supported in the mainframe; a print head unit supported in the main unit so as to bepivotable between an image-forming state and a non-image forming state,the print head unit being pressed against the platen roller to convey asheet therebetween when the print head unit is in the image-formingstate; a sheet case adapted to accommodate a sheet, the sheet case beingdesigned to be mounted in between the first and second side plates ofthe main frame through the insertion part, the sheet case including asheet feeder, a sheet take-up unit, and a linking unit that links thesheet feeder and the sheet take-up unit; a contact portion that isattached to the print head unit so as to pivot together with the printhead unit, the contact portion contacting the linking unit of the sheetcase from a second side plate side and at least one of the contactportion and the linking unit of the sheet case being elasticallydeformed when the print head unit is in the image-forming state; a guideunit that is coupled to the print head unit and is adapted to guide thesheet being conveyed, the contact portion being formed unitarily withthe guide unit; and a locking member that is provided in the second sideplate of the main frame and designed to disengageably engage the sheetcase.